Matthew Greene, a former member of the Proud Boys from New York, pleaded guilty Wednesday to federal conspiracy and obstruction charges, a big break in the Justice Department’s prosecution of extremist groups that participated in or led the Jan. 6 Capitol insurrection. Greene, 34, also “agreed to cooperate with the government — potentially against other members of the far-right extremist group,” The New York Times reports.

Greene traveled to Washington on Jan. 5 with a fellow upstate New York Proud Boy, Dominic Pezzola, and a third, William Pepe, slept on the floor of his hotel room, according to Greene’s plea. Greene said he helped program earpiece-fitted handheld radios belonging to Pezzola that Proud Boys used to communicate during the Capitol siege. All three men were indicted on the same conspiracy charges in April; Pezzola and Pepe have pleaded not guilty.

Prosecutors say the Proud Boys took a lead role in storming the Capitol on Jan. 6. In his plea, Greene said he and Pezzola were “among the first wave to cross the downed police line” and climb scaffolding up to higher tiers of the Capitol. Greene said he left after police began pushing back with chemical irritants, but Pezzola continued up the steps and, according to prosecutors, used a police shield to break a window and enter the Capitol. You can watch him in a Wall Street Journal video following the Proud Boys’ trail on Jan. 6

After the riot, Greene boasted that “we took the capital” [sic], and later urged other Proud Boys on an encrypted channel to “take back our country” and “stand together now or end up in the gulag separately,” according to court records. Greene subsequently concluded “his personal beliefs and ethics do not align with those of the Proud Boys” and “is anxious to publicly disavow his brief membership in this group,” his lawyer says.

Greene is scheduled to be sentenced on March 10. He faces up to 25 years in prison but will probably get closer to 41 to 51 months because of his cooperation with investigators.

Federal prosecutors have charged more than 700 people with federal crimes related to the Jan. 6 riot, and more than 150 have pleaded guilty, including two others with Proud Boy ties and at least five members of another extremist group, the Oath Keepers. One of those Oath Keepers, Graydon Young, pleaded guilty to conspiracy charges.